A typical rotating turbine wheel consists of a central hub and a series of airfoil blades projecting radially from the hub. In the case of a metal turbine wheel, one of the manufacturing techniques used is the investment casting process which requires a preformed pattern of wax or any other suitable material. In cases where metal cores cannot be separated from the pattern due to backlock, the pattern is produced by making individual blade portions which are fused together in elaborate assembly fixtures. An inherent disadvantage of this method is the amount of time required to mold the blades separately, and to assemble and bond them together in a wheel. In addition, elaborate assembly fixtures are necessary to produce an assembled wheel that is within acceptable tolerance specifications.
Another method to produce wax patterns for such a turbine wheel is by using individual soluble wax inserts in a die where the wax is injected and the solubles are removed by dissolving them in a suitable solvent. This method has the disadvantage of (1) the time required to inject the soluble inserts, (2) the loss of the soluble material after it is dissolved, and (3) the inaccuracy of the soluble inserts resulting from shrinkage and distortion during the molding process of the soluble inserts.
An object of this invention is to eliminate the necessity of producing and assembling individual airfoil portions or segments for production of investment casting patterns of the sort described. This is done by making a two-piece hub and blade complex which is split approximately through the axial center of the complex. The airfoil blades may be an integral part of the hub, with every other blade appearing on each half of the complex. The two hub halves are then meshed together and fused to form a complete wheel pattern with exact spacing of adjacent blades which, as mentioned above, might overlap each other in a circumferential direction.
It will be made apparent in this specification that it is much more economical to mold two halves and bond them together than it is to mold a plurality of blades and use a sophisticated assembly fixture for positioning and bonding them together. For example, a forty blade turbine wheel would require forty separate blades as opposed to using this invention which requires only two halves, each containing twenty blades.
It will also be obvious from the following specification that this invention is applicable to other turbine wheels that are not necessarily made out of metal but are manufactured by the investment casting process. For example, such process may be applicable to manufacture turbine wheels made from ceramic materials.
Other objects and advantages of this invention will be apparent from the accompanying specification and drawings and the essential features thereof will be set forth in the appended claims.